Multiple winding alternators to supply electrical loads are well known. In automotive application it is customary to provide three-phase alternating current generators, driven by the engine of the vehicle. The three-phase output is rectified in a rectifier bank to charge a battery and to supply electrical loads, connected in parallel to the battery through suitable switching arrangements. Voltage is maintained at the proper level for the battery by means of a voltage regulator which may be a solid-state controller, controlling current flow through the field of the alternator in pulses of varying duty cycle so that the voltage output of the alternator is essentially independent of loading thereon or speed of the driving internal combustion (IC) engine.
The increasing electrical loads placed on mobile self-contained electrical supply systems installed, for example, in automotive vehicles, boats, and the like, require supply currents of increasing level. Some loads are particularly demanding of current, for example heaters used for electrical heating of passenger spaces of vehicles, windshield and other window area heaters, air-conditioning apparatus, and the like. The alternator must be so designed that it is capable of supplying electrical currents to all loads, although peak demands thereon, for example for heating or air-conditioning, are placed on the alternator only rarely and seasonally.
It has been proposed to so design the alternator that it has a main winding, the power capacity of which is matched to the normally expected load to be placed thereon, and to wind an additional or auxiliary armature winding on the alternator which is used to supply current for peak demands. This auxiliary winding, in the past, was idle during normal operation. The increased complexity of such an arrangement, and the necessity of providing separate terminals, ground connections and the like, increases the cost of such an arrangement and it is uneconomical to provide such a dual arrangement if the use of the second or auxiliary winding is only occasional or temporary. The main winding of the alternator did not contribute to the energy supply of the additional loads although just at that time the main portion of the alternator may not be loaded to its limit.